1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to circuit breakers, such as a molded case circuit breaker including an arc chamber and a gas discharge filter for avoiding inadvertent flow of electrical current due to ionized exhaust gases being discharged from the arc chamber. The invention also relates to gas discharge filters for electrical switching apparatus.
2. Background Information
Electrical switching apparatus include, for example, circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers.
Circuit breakers are used to protect electrical circuitry from damage due to an over current condition, such as an overload condition or a relatively high level short circuit or fault condition. Circuit breakers typically have a molded plastic housing enclosing at least one pair of separable contacts which are operated either manually by way of a handle disposed on the outside of the housing or automatically by way of an internal trip unit in response to an over current condition.
When the circuit breaker separable contacts are opened under overload, short circuit or fault conditions, an arc is usually created which is accompanied by the generation of ionized gases. The ionized gases are conductive. If these ionized gases collect in the vicinity of the line terminals of the circuit breaker, they may cause a phase-to-phase electrical failure between the circuit breaker terminals, and/or a phase-to-ground electrical failure with any metallic enclosure within which the circuit breaker is mounted. This can lead to electrical faults on the line side of the circuit breaker and damage to switchgear equipment.
Circuit breakers typically include vents to allow the ionized gases to quickly escape therefrom. The problem of electrical faults is especially acute where the poles of the circuit breaker are in close proximity to the circuit breaker vents, thus subjecting each pole of the circuit breaker to hot ionized and electrically conductive exhaust gases. Accordingly, there is a need for preventing these kinds of electrical breakdowns.
Known prior art devices for preventing electrical faults caused by conductive ionized gases include gas deflectors, shields, and dampers.
U.S. Pat. No. 4,639,564 discloses a tubular wall in the cover of a circuit breaker which surrounds a terminal screw. The tubular wall includes a biased end face with the lower end of the face being disposed between the screw and the opening in a wall of a cover. This biased end face provides a cooling effect caused by siphoning or inward flow of air from the top of the tubular wall downwardly through the tubular wall and around the terminal screw from where it exhausts into the atmosphere through an outlet. Although the disclosure teaches the cooling of the gases by siphoning fresh air and mixing it with hot gases, the exhaust gases still remain relatively hot.
U.S. Pat. No. 4,650,940 discloses a circuit breaker having a flap or barrier, which is disposed within a terminal compartment and over the inner side of an opening for a screwdriver. The ionized gases flowing into the terminal compartment are stopped from flowing through the opening by the flap extending there across. The flap is preferably composed of a sheet of fiber or fiber type material, which is chemically and electrically impervious to hot ionized gases. However, because the shield is not fixed, it may move within the circuit breaker housing or be accidentally removed, thereby allowing a path for ionized gases to reach ground through the screwdriver opening.
U.S. patent application Ser. No. 09/919,474, filed Jul. 31, 2001, discloses an exhaust control device for reducing the temperature, velocity, and ionization level of gases produced in a circuit interrupter, specifically a fuse, upon interruption of a circuit. Ionized gases flow from the fuse into a casing having first and second expansion chambers configured to separate gases into first and second pressure waves that sequentially travel through a mesh heat sink and then a damper to reduce gas temperature, velocity, and ionization level. However, the disclosed exhaust device is complex and cumbersome, and therefore, not conducive for use in applications such as, for example, circuit breakers mounted within a switchgear cabinet (e.g., without limitation, a panel board or a load center), particularly multi-pole circuit breakers having an ionized gas exhaust vent at each pole.
Accordingly, there is room for improvement in gas discharge filters for electrical switching apparatus and in circuit breakers employing ionized gas discharge filters.
These needs and others are satisfied by the present invention, which is directed to a gas discharge filter for an electrical switching apparatus. The filter cools ionized gases discharged from an arc chamber in order to minimize electrical faults associated therewith.
As one aspect of the invention, a gas discharge filter is used with an electrical switching apparatus including a line side with line terminal means, a load side with load terminal means, separable contacts electrically connected in series between the line terminal means and the load terminal means, a housing, an arc chamber within the housing and structured to extinguish an arc between the separable contacts when opened, the housing having an exhaust vent opening for discharging through an exhaust path ionized gases which are developed from the arc, the ionized gases having a temperature. The gas discharge filter comprises: heat reduction means for reducing the temperature of the discharged ionized gases, and a supporting member for securing the heat reduction means outside the housing and proximate the exhaust vent opening in the exhaust path for the discharged ionized gases.
The heat reduction means may include a heat exchanger including a conductive insert member structured for removable insertion within the supporting member.
As another aspect of the invention, an electrical switching apparatus comprises: at least one line terminal; at least one load terminal; at least one pair of separable contacts electrically connected in series between the at least one line terminal and the at least one load terminal; a housing; at least one arc chamber within the housing and structured to extinguish an arc between the separable contacts when opened; the housing having at least one exhaust vent opening for discharging through at least one exhaust path ionized gases which are developed from the arc; the ionized gases having a temperature; and a gas discharge filter comprising: heat reduction means for reducing the temperature of the discharged ionized gases, and a supporting member for securing the heat reduction means outside the housing and proximate the at least one exhaust vent opening, in the exhaust path for the discharged ionized gases.
As another aspect of the invention, a power distribution system comprises: a switchgear cabinet, an electrical switching apparatus coupled to the switchgear cabinet, the electrical switching apparatus including at least one line terminal, at least one load terminal, at least one pair of separable contacts electrically connected in series between the at least one line terminal and the at least one load termninal, a housing, at least one arc chamber within the housing and structured, to extinguish an arc between the separable contacts when opened, the housing having at least one exhaust vent opening for discharging through at least one exhaust path ionized gases which are developed from the arc, the ionized gases having a temperature, and a gas discharge filter comprising: heat reduction means for reducing the temperature of the discharged ionized gases, and a supporting member for securing the heat reduction means outside the housing and proximate the at least one exhaust vent opening, in the exhaust path for the discharged ionized gases.
The switchgear cabinet may include a securing element structured to secure the supporting member to the switchgear cabinet.